690 PKOCEEDINGS OF THE AJIERICAN ACADEMY. 



This method, however, is not practicable for any but small amounts, 

 and there is danger of contamination by the moisture of the air. 



In the preparation of chlorsulphonic acid the best method is the 

 treatment of sulphur trioxide with hydrochloric acid, which must be 

 ascribed to A. Williamson, ^^ though first put in practical form by 

 Beckurts and Otto.*^ Most convenient is a liquid oleum containing 

 as much sulphur trioxide as possible according to the reaction : 



H2SO4 + SO, + HCl = H3SO4 + SO3HCI. 



No pyrosulphuryl chloride can be formed, and the product is made 

 practically pure by distillation with hydrochloric acid. 



While chlorsulphonic acid may be formed under certain conditions 

 by the addition of water to pyrosulphuryl chloride, the reaction does 

 not serve as a method of preparation. Similarly, though dehydration 

 of chlorsulphonic acid by phosphorus pentoxide takes place, it is only 

 partial and hence of no advantage as a means of preparing pyrosul- 

 phuryl chloride. 



The Preparation of Pyrosulphuryl Chloride. 



The procedure adopted by us in treating sulphur trioxide with car- 

 bon tetrachloride according to the method of Scblitzenberger is as 

 follows : — A round-bottomed flask of suitable size is sealed to the 

 tube of an upright condenser, the upper end of the tube being carried 

 some distance above the jacket of the condenser. A few centimeters 

 below the top of the tube is sealed a side-tube of smaller bore, leading 

 to a flue. An absorption bottle for the phosgene may be used here if 

 desired. Through a rubber stopper in the top of the condenser tube 

 and leading below the side-tube passes a separating funnel. 



The oleum is prepared from an ordinary fuming acid by the addition 

 of the requisite amount of solid sulphur trioxide, the proportion of the 

 last in the mixture being determined by titration. For analysis, the 

 oleum is weighed in a thin glass bulb, sealed after being filled. The 

 bulb is broken under considerable water in a tightly stoppered bottle, 

 the contents of which, when homogeneous, are made up to a definite 

 volume. The carbon tetrachloride is a crude commercial product, 

 dried over calcic chloride. 



The dry apparatus is placed on a steam bath and carbon tetra- 

 chloride added through the condenser tube. The separating funnel 

 containing the oleum is placed in position. The flask is then heated 

 gradually and the oleum is run in slowly, the rate of addition being 

 governed by the evolution of phosgene. After the addition of the 



